1. Field of the Invention
The present invention relates to a safety switch which is mounted on the wall surface of a doorway of a room in which, for example, industrial machinery is installed, and which stops the power supply to the industrial machinery, etc. when the door of the doorway is opened.
2. Description of the Related Art
In a hazardous zone of the rooms or plants in which industrial machinery is installed, or industrial machinery itself, a system for locking the drive of the machine is required to be installed when the door of the doorway in the room or a danger zone is not completely closed, in order to prevent troubles in which workers are caught in by the machine and injured.
For such a lock system, conventionally, a system has been adopted to install limit switches at the sliding portions of the door and to supply power to the industrial machinery installed in the room only when the door closed condition is detected by the limit switches.
However, according to this kind of system, operating the actuator of the limit switch without closing the door enables the operation of the machines in the room, and it cannot be said to be a perfect safety measure.
Therefore, the inventor has already proposed a safety switch which has a construction for preventing this kind of misoperation (Japanese Non-examined Patent Publication No. Hei 6-76674).
The safety switch of this proposal is a switch which has a construction in which the special-purpose of the actuator fixed to the door enters the operating portion of the switch proper mounted to the wall surface in the circumference of the doorway of the room when the door of the doorway is closed, and with this action, the mobile contact of the contact block is changed over, and with this kind of change-over operation, the circuit connection is changed over to the main circuit side (power supply circuit to industrial machinery), causing the machines inside the room to be ready for operation.
Now, there is no special problem in functions, safety, etc. with the existing safety switch, etc. stated in the Japanese Non-examined Patent No. Hei 6-76674, but according to the proposed safety switch, because a driving cam and restricted cam (both are plate cams) with groove cams formed, respectively, are arranged at the operating portion, the rotating phase difference is provided between the driving cam and the restricted cam, and all the cams are rotated to change over the connection contacts of the switch portion only when the special-purpose actuator enters the operating portion, it is inevitable that the profile, processing, etc. of each cam be complicated, and if there is any deviation in positional relationship of groove cams between the driving cam and the restricted cam, there is a fear of causing maloperation, and it is essential to process the groove cam of each cam at high accuracy.